1. Field of the Invention
The present invention relates to a diaphragm control apparatus for a lens of a CCTV (Closed Circuit Television) camera, wherein the control can be switched between an automatic control mode and a remote control mode.
2. Description of the Related Art
In a known diaphragm control apparatus for a lens of a CCTV camera, in which a movable magnet servo meter or movable coil servo meter is used as a diaphragm driving source, an automatic control in which the diaphragm is automatically controlled in accordance with an image signal sent from the CCTV camera and a remote control in which the diaphragm can be remotely set at an optional position, regardless of the image signal from the CCTV camera, can be optionally selected depending on the conditions of use.
In the remote control mode, a control signal is supplied to a drive meter of a servo meter from an external remote controller to control the diaphragm so as to set an optional diaphragm position regardless of the image signal from the CCTV camera, and a position detection signal output from a position detection device of the servo meter is fed back to the drive meter to hold the diaphragm in the selected position.
However, since the diaphragm is electrically controlled, if electricity supply from the CCTV camera is interrupted, it is impossible to hold the diaphragm at an optional position, so that the diaphragm is returned to a predetermined initial position. Consequently, a user must troublesomely reset the diaphragm each time the power source is turned ON.